MBProgressHUD not showing

In my app, I am loading a resource heavy view that takes about 1 to 2 seconds to load. So I am loading it in a separate thread like this:

hud = [[MBProgressHUD alloc] init];
[hud showWhileExecuting:@selector(loadWorkbench:) onTarget:self withObject:nil animated:YES];

however it never appears, and application looks frozen to the end user. any ideas where I have gone wrong?

Yes. It does not appear because you never tell add the HUD as a subview of the window. try something like:

    // Should be initialized with the windows frame so the HUD disables all user input by covering the entire screen
    HUD = [[MBProgressHUD alloc] initWithWindow:[UIApplication sharedApplication].keyWindow];

    // Add HUD to screen
    [self.view.window addSubview:HUD];

    // Register for HUD callbacks so we can remove it from the window at the right time
    HUD.delegate = self;

    HUD.labelText = NSLocalizedString(@"Loading Workbench", nil);
    HUD.detailsLabelText = NSLocalizedString(@"please wait", nil);

    // Show the HUD while the provided method executes in a new thread
    [HUD showWhileExecuting:@selector(loadWorkbench:) onTarget:self withObject:nil animated:YES];

Since you are setting yourself as the HUD delegate, also add the following delegate method:

- (void)hudWasHidden {
    // Remove HUD from screen 
    [HUD removeFromSuperview];

    // add here the code you may need

}

and remember to add MBProgressHUDDelegate in the corresponding header file.